As a configuration for driving a ram (slider) movable by a fluid pressure machine, a configuration for reciprocally driving a ram, a table or the like that is one example of a slide is adopted in a press machine (pressurizer) of various types, and a configuration for reciprocating a moving member of various types is adopted in a bending processing machine, a machine tool or the like of various types.
Further, for example, a configuration of a fluid pressure machine in a press machine for reciprocally moving a ram (slider) including a large-diameter cylinder and a small-diameter cylinder, and a reciprocable piston rod included in the small-diameter cylinder using a mechanical configuration such as a ball screw mechanism, thereby supplying a working fluid in the small-diameter cylinder to the large-diameter cylinder and obtaining significant power is disclosed in Japanese Patent Application Laid-Open No. 2002-295624 (Patent Document 1), for example.
As shown in FIG. 1, in the configuration of the Patent Document 1, the fluid pressure machine is configured so that a large-diameter cylinder 101 is provided, the large-diameter cylinder 101 includes therein a large-diameter piston 101P, and so that a large-diameter piston rod 101R protrudes from one side of the large-diameter piston 101P to serve as a ram. An interior of the large-diameter cylinder 101 is divided into a piston-side first compartment 101A and a piston rod-side second compartment 101B by the piston 101P.
Further, a small-diameter cylinder 103 is provided to supply a pressurized working fluid to the large-diameter cylinder 101. An interior of the small-diameter cylinder 103 is divided into a piston-side first compartment 103A and a piston rod-side second compartment 103B by a small-diameter piston 103P. A piston rod 103R provided on one side of the small-diameter piston 103P integrally is connected to a moving member 107 such as a ball nut reciprocably provided in a ball screw mechanism 105 rotation-driven by a motor M such as a servo motor.
The first compartment 101A of the large-diameter cylinder 101 is connected to the first compartment 103A of the small-diameter cylinder 103 by a connection path 109. The second compartment 101B of the large-diameter cylinder 101 is connected to the second compartment 103B of the small-diameter cylinder 103 by a connection path 111. An accumulator 113 is connected to the connection path 111.
By so configuring the fluid pressure machine, if the motor M is driven to press and move the small-diameter piston rod 103R upward, the working fluid in the first compartment 103A of the small-diameter cylinder 103 is supplied into the first compartment 101A of the large-diameter cylinder 101. The large-diameter piston 101P and the large-diameter piston rod 101R are moved downward, accordingly. The working fluid in the second compartment 101B of the large-diameter cylinder 101 flows into the second compartment 103B of the small-diameter cylinder 103. In an opposite operation, the working fluid in the second compartment 103B of the small-diameter cylinder 103 flows into the second compartment 101B of the large-diameter cylinder 101, and mat in the first compartment 101A in the large-diameter cylinder 101 flows into the first compartment 103A of the small-diameter cylinder 103.
As described above, during inflow and outflow of the working fluid between the first compartments 101A and 103A of the large-diameter cylinder 101 and the small-diameter cylinder 103 and between the second compartments 101B and 103B thereof, respectively, if it is assumed that a flow rate of each of the first compartments 101A and 103A is Q1 and that of each of the second compartments 101B and 103B is Q2, then a relationship of Q1>Q2 is satisfied, and Q1/Q2 needs to have a constant relationship.
Therefore, it is necessary to keep a pressure reception area ratio NA of the first compartment 101A to the second compartment 101B of the large-diameter cylinder 101 and a pressure reception area ratio NB of the first compartment 103A to the second compartment 103B of the small-diameter cylinder 103 to satisfy a relationship of NA=NB. Accordingly, if the large-diameter cylinder 101 is selected by, for example, a pressurization capability or the like of the press machine, the small-diameter cylinder 103 is decided uniquely to correspond to the large-diameter cylinder 101, thus disadvantageously restricting a degree of freedom for design.
Moreover, with the above-described configuration, the working fluid supplied from the small-diameter cylinder 103 enables the large-diameter piston rod 101R to reciprocate. Due to this, to make a stroke length of the large-diameter piston rod 101R large, it is disadvantageously necessary to increase a length of the small-diameter cylinder 103. Besides, if the large-diameter piston rod 101R is to move at high velocity, the velocity of the large-diameter piston rod 101R cannot be set almost equal to a moving velocity of the small-diameter piston rod 103R, thereby hampering improvement in efficiency by high-velocity movement of the ram.
Furthermore, with the conventional configuration, the working fluid such as working oil is simply filled up into the first compartment 101A and the second compartment 101B of the large-diameter cylinder 101 and the first compartment 103A and the second compartment 103B of the large-diameter cylinder 103. Due to this, to make power of the large-piston rod 101R large, it takes a relatively long time to raise an internal pressure of the first compartment 101A of the large-diameter cylinder 101 to a desired pressure, thereby disadvantageously hampering the improvement in efficiency.
The conventional fluid pressure machine is configured to reciprocate the large-diameter piston rod 101R while the large-diameter cylinder 101 is fixed. Due to this, a moving position of the large-diameter piston rod 101R relative to a fixing unit, such as a frame, fixing the large-diameter cylinder can be detected relatively easily. However, if it is configured so that the large-diameter piston rod 101R is fixed to the fixing unit and the large-diameter cylinder 101 is moved relative to the fixing unit, a position of the large-diameter cylinder 101 cannot be detected accurately only by detecting a rotation of the motor M. Therefore, a problem occurs that an expensive linear sensor or the like needs to be arranged between the fixing unit and the large-diameter cylinder 101.
The present invention has been achieved to solve the problems described above, and an object of the invention is to provide a ram position detection method, a ram driving method, a ram driving apparatus, and a press machine including the ram driving apparatus capable of normally moving a ram at high velocity and causing the ram to operate at low velocity when the ram performs a pressurization operation.